Re: [PATCHv2 bpf-next 1/2] bpf: Do not allow to load sleepable BPF_TRACE_RAW_TP program

[Jiri Olsa <olsajiri@gmail.com>]

On Sun, Jan 15, 2023 at 01:21:48PM -0800, Alexei Starovoitov wrote:
> On Wed, Jan 11, 2023 at 2:11 AM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > Currently we allow to load any tracing program as sleepable,
> > but BPF_TRACE_RAW_TP can't sleep. Making the check explicit
> > for tracing programs attach types, so sleepable BPF_TRACE_RAW_TP
> > will fail to load.
> >
> > Updating the verifier error to mention iter programs as well.
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> > v2 changes:
> >   - use bool for can_be_sleepable return value [Song]
> >   - add tests [Song]
> >
> >  kernel/bpf/verifier.c | 17 ++++++++++++++---
> >  1 file changed, 14 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index fa4c911603e9..f20777c2a957 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -16743,6 +16743,18 @@ BTF_ID(func, rcu_read_unlock_strict)
> >  #endif
> >  BTF_SET_END(btf_id_deny)
> >
> > +static bool can_be_sleepable(struct bpf_prog *prog)
> > +{
> > +       if (prog->type == BPF_PROG_TYPE_TRACING) {
> > +               return prog->expected_attach_type == BPF_TRACE_FENTRY ||
> > +                      prog->expected_attach_type == BPF_TRACE_FEXIT ||
> > +                      prog->expected_attach_type == BPF_MODIFY_RETURN ||
> > +                      prog->expected_attach_type == BPF_TRACE_ITER;
> > +       }
> > +       return prog->type == BPF_PROG_TYPE_LSM ||
> > +              prog->type == BPF_PROG_TYPE_KPROBE;
> > +}
> 
> imo it's too verbose.
> Maybe try a switch stmt ?
> Or at least copy prog->expected_attach_type and prog->type into variables.

ok, the switch seems better, I'll send new version

thanks,
jirka


---
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fa4c911603e9..966dbfc14288 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -16743,6 +16743,23 @@ BTF_ID(func, rcu_read_unlock_strict)
 #endif
 BTF_SET_END(btf_id_deny)
 
+static bool can_be_sleepable(struct bpf_prog *prog)
+{
+	if (prog->type == BPF_PROG_TYPE_TRACING) {
+		switch (prog->expected_attach_type) {
+		case BPF_TRACE_FENTRY:
+		case BPF_TRACE_FEXIT:
+		case BPF_MODIFY_RETURN:
+		case BPF_TRACE_ITER:
+			return true;
+		default:
+			return false;
+		}
+	}
+	return prog->type == BPF_PROG_TYPE_LSM ||
+	       prog->type == BPF_PROG_TYPE_KPROBE;
+}
+
 static int check_attach_btf_id(struct bpf_verifier_env *env)
 {
 	struct bpf_prog *prog = env->prog;
@@ -16761,9 +16778,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 		return -EINVAL;
 	}
 
-	if (prog->aux->sleepable && prog->type != BPF_PROG_TYPE_TRACING &&
-	    prog->type != BPF_PROG_TYPE_LSM && prog->type != BPF_PROG_TYPE_KPROBE) {
-		verbose(env, "Only fentry/fexit/fmod_ret, lsm, and kprobe/uprobe programs can be sleepable\n");
+	if (prog->aux->sleepable && !can_be_sleepable(prog)) {
+		verbose(env, "Only fentry/fexit/fmod_ret, lsm, iter and kprobe/uprobe programs can be sleepable\n");
 		return -EINVAL;
 	}